Synechococcus Cells Research Articles

Temporal and spatial diversity and abundance of cryptophytes in San Diego coastal waters.

Cryptophytes (class Cryptophyceae) are bi-flagellated eukaryotic protists with mixed nutritional modes and cosmopolitan distribution in aquatic environments. Despite their ubiquitous presence, their molecular diversity is understudied in coastal waters. Weekly 18S rRNA gene amplicon sequencing at the Scripps Institution of Oceanography pier (La Jolla, California) in 2016 revealed 16 unique cryptophyte amplicon sequence variants (ASVs), with two dominant "clade 4" ASVs. The diversity of cryptophytes was lower than what is often seen in other phytoplankton taxa. One ASV represented a known Synechococcus grazer, while the other one appeared not to have cultured representatives and an unknown potential for mixotrophy. These two dominant ASVs were negatively correlated, suggesting possible niche differentiation. The cryptophyte population in nearby San Diego Bay was surveyed in 2019 and showed the increasing dominance of a different clade 4 ASV toward the back of the bay where conditions are warmer, saltier, and shallower relative to other areas in the bay. An ASV representing a potentially chromatically acclimating cryptophyte species also suggested that San Diego Bay exerts differing ecological selection pressures than nearby coastal waters. Cryptophyte and Synechococcus cell abundance at the SIO Pier from 2011 to 2017 showed that cryptophytes were consistently present and had a significant correlation with Synechococcus abundance, but no detectable seasonality. The demonstrated mixotrophy of some cryptophytes suggests that grazing on these and perhaps other bacteria is important for their ecological success. Using several assumptions, we calculated that cryptophytes could consume up to 44% (average 6%) of the Synechococcus population per day. This implies that cryptophytes could significantly influence Synechococcus abundance.

Differential acclimation kinetics of the two forms of type IV chromatic acclimaters occurring in marine Synechococcus cyanobacteria.

Synechococcus, the second most abundant marine phytoplanktonic organism, displays the widest variety of pigment content of all marine oxyphototrophs, explaining its ability to colonize all spectral niches occurring in the upper lit layer of oceans. Seven Synechococcus pigment types (PTs) have been described so far based on the phycobiliprotein composition and chromophorylation of their light-harvesting complexes, called phycobilisomes. The most elaborate and abundant PT (3d) in the open ocean consists of cells capable of type IV chromatic acclimation (CA4), i.e., to reversibly modify the ratio of the blue light-absorbing phycourobilin (PUB) to the green light-absorbing phycoerythrobilin (PEB) in phycobilisome rods to match the ambient light color. Two genetically distinct types of chromatic acclimaters, so-called PTs 3dA and 3dB, occur at similar global abundance in the ocean, but the precise physiological differences between these two types and the reasons for their complementary niche partitioning in the field remain obscure. Here, photoacclimation experiments in different mixes of blue and green light of representatives of these two PTs demonstrated that they differ by the ratio of blue-to-green light required to trigger the CA4 process. Furthermore, shift experiments between 100% blue and 100% green light, and vice-versa, revealed significant discrepancies between the acclimation pace of the two types of chromatic acclimaters. This study provides novel insights into the finely tuned adaptation mechanisms used by Synechococcus cells to colonize the whole underwater light field.

The Specificities of Lysophosphatidic Acid Acyltransferase and Fatty Acid Desaturase Determine the High Content of Myristic and Myristoleic Acids in Cyanobacterium sp. IPPAS B-1200.

The cyanobacterial strain Cyanobacterium sp. IPPAS B-1200 isolated from Lake Balkhash is characterized by high relative amounts of myristic (30%) and myristoleic (10%) acids. The remaining fatty acids (FAs) are represented mainly by palmitic (20%) and palmitoleic (40%) acids. We expressed the genes for lysophosphatidic acid acyltransferase (LPAAT; EC 2.3.1.51) and Δ9 fatty acid desaturase (FAD; EC 1.14.19.1) from Cyanobacterium sp. IPPAS B-1200 in Synechococcus elongatus PCC 7942, which synthesizes myristic and myristoleic acids at the level of 0.5-1% and produces mainly palmitic (~60%) and palmitoleic (35%) acids. S. elongatus cells that expressed foreign LPAAT synthesized myristic acid at 26%, but did not produce myristoleic acid, suggesting that Δ9-FAD of S. elongatus cannot desaturate FAs with chain lengths less than C16. Synechococcus cells that co-expressed LPAAT and Δ9-FAD of Cyanobacterium synthesized up to 45% palmitoleic and 9% myristoleic acid, suggesting that Δ9-FAD of Cyanobacterium is capable of desaturating saturated acyl chains of any length.

Engineering Cyanobacterial Cell Factories for Photosynthetic Production of Fructose.

Fructose is an important monosaccharide product widely applied in the food, medicine, and chemical industries. Currently, fructose is mainly manufactured with plant biomass-sourced polysaccharides through multiple steps of digestion, conversion, separation, and purification. The development of cyanobacterial metabolic engineering provides an attractive alternative route for the one-step direct production of fructose utilizing carbon dioxide and solar energy. In this work, we developed a paradigm for engineering cyanobacterial chassis cells into efficient cell factories for the photosynthetic production of fructose. In a representative cyanobacterial strain, Synechococcus elongatus PCC 7942, knockout of fructokinase effectively activated the synthesis and secretion of fructose in hypersaline conditions, independent of any heterologous transporters. The native sucrose synthesis pathway was identified as playing a primary role in fructose synthesis. Through combinatory optimizations on the levels of metabolism, physiology, and cultivation, the fructose yield of the Synechococcus cell factories was stepwise improved to 3.9 g/L. Such a paradigm was also adopted to engineer another Synechococcus strain, the marine species Synechococcus sp. PCC 7002, and facilitated an even higher fructose yield of over 6 g/L. Finally, the fructose synthesized and secreted by the cyanobacterial photosynthetic cell factories was successfully extracted and prepared from the culture broth in the form of products with 86% purity through multistep separation-purification operations. This work demonstrated a paradigm for systematically engineering cyanobacteria for photosynthetic production of desired metabolites, and it also confirmed the feasibility and potential of cyanobacterial photosynthetic biomanufacturing as a simple and efficient route for fructose production.

Effect of Clay Minerals on Carbonate Precipitation Induced by Cyanobacterium Synechococcus sp.

Carbonate precipitation induced by cyanobacteria is an important factor in lacustrine fine-grained carbonate rock genesis. As key components of these rocks, clay minerals play an important role in aggregating cyanobacteria. However, the formation mechanism of fine-grained carbonate under the effect of clay minerals is unclear. In this study, we investigated carbonate precipitation by Synechococcus cells under the influence of clay minerals. The results showed that clay minerals can accelerate Synechococcus aggregation, and the aggregation rate of the kaolinite group was significantly higher than that of montmorillonite. The aggregate size and Synechococcus cell content increased with an increase in clay minerals, resulting in increasing organic matter and carboxyl content in the aggregates. Due to the high affinity between carboxyl and Ca2+, the presence of Synechococcus sp. could improve the Mg/Ca molar ratio in the microenvironment of aggregates, which is conducive to aragonite precipitation. Thus, aragonite 5 to 10 μm in size precipitated when Synechococcus and clay minerals coexisted, whereas low-magnesium calcite (15 to 60 μm) was the main carbonate only in the presence of Synechococcus. This study provides important insights into the mechanisms of microbial-induced carbonate precipitation under the effect of clay minerals, which might offer theoretical support for the genesis of fine-grained lacustrine carbonate. IMPORTANCE The biogenesis of lacustrine fine-grained carbonates is of great significance to the exploitation of shale oil. Clay minerals are an important component of lacustrine fine-grained sedimentary rocks, which is conductive to the aggregation and settlement of cyanobacteria. We investigated the precipitation of carbonate induced by Synechococcus sp. with the addition of kaolinite and montmorillonite. The pH and calcium carbonate saturation of the environment increased under the effect of cyanobacteria photosynthesis. The aggregation of cyanobacteria cells increased the Mg/Ca molar ratio of the microenvironment, creating a favorable condition for the precipitation of aragonite, which was similar in size to the micritic calcite of fine-grained sedimentary rocks. This study provides theoretical support for the genesis of fine-grained carbonates.

Photoinhibition of the Picophytoplankter Synechococcus Is Exacerbated by Ocean Acidification

The marine picocyanobacterium Synechococcus accounts for a major fraction of the primary production across the global oceans. However, knowledge of the responses of Synechococcus to changing pCO2 and light levels has been scarcely documented. Hence, we grew Synechococcus sp. CB0101 at two CO2 concentrations (ambient CO2 AC:410 μatm; high CO2 HC:1000 μatm) under various light levels between 25 and 800 μmol photons m−2 s−1 for 10–20 generations and found that the growth of Synechococcus strain CB0101 is strongly influenced by light intensity, peaking at 250 μmol m−2 s−1 and thereafter declined at higher light levels. Synechococcus cells showed a range of acclimation in their photophysiological characteristics, including changes in pigment content, optical absorption cross section, and light harvesting efficiency. Elevated pCO2 inhibited the growth of cells at light intensities close to or greater than saturation, with inhibition being greater under high light. Elevated pCO2 also reduced photosynthetic carbon fixation rates under high light but had smaller effects on the decrease in quantum yield and maximum relative electron transport rates observed under increasing light intensity. At the same time, the elevated pCO2 significantly decreased particulate organic carbon (POC) and particulate organic nitrogen (PON), particularly under low light. Ocean acidification, by increasing the inhibitory effects of high light, may affect the growth and competitiveness of Synechococcus in surface waters in the future scenario.

Engineering cyanobacteria for converting carbon dioxide into isomaltulose

Isomaltulose is a promising functional sweetener with broad application prospects in the food industry. Currently, isomaltulose is mainly produced through bioconversion processes based on the isomerization of sucrose, the economic feasibility of which is influenced by the cost of sucrose feedstocks, the biocatalyst preparation, and product purification. Cyanobacterial photosynthetic production utilizing solar energy and carbon dioxide represents a promising route for the supply of sugar products, which can promote both carbon reduction and green production. Previously, some cyanobacteria strains have been successfully engineered for synthesis of sucrose, the main feedstock for isomaltulose production. In this work, we introduced different sucrose isomerases into Synechococcus elongatus PCC 7942 and successfully achieved the isomaltulose synthesis and accumulation in the recombinant strains. Combinatory expression of an Escherichia coli sourced sucrose permease CscB with the sucrose isomerases led to efficient secretion of isomaltulose and significantly elevated the final titer. During a 6-day cultivation, 777 mg/L of isomaltulose was produced by the engineered Synechococcus cell factory. This work demonstrated a new route for isomaltulose biosynthesis utilizing carbon dioxide as the substrate, and provided novel understandings for the plasticity of cyanobacterial photosynthetic metabolism network.

Acclimation of the photosynthetic apparatus to low light in a thermophilic Synechococcus sp. strain.

Depending upon their growth responses to high and low irradiance, respectively, thermophilic Synechococcus sp. isolates from microbial mats associated with the effluent channels of Mushroom Spring, an alkaline siliceous hot spring in Yellowstone National Park, can be described as either high-light (HL) or low-light (LL) ecotypes. Strains isolated from the bottom of the photic zone grow more rapidly at low irradiance compared to strains isolated from the uppermost layer of the mat, which conversely grow better at high irradiance. The LL-ecotypes develop far-red absorbance and fluorescence emission features after growth in LL. These isolates have a unique gene cluster that encodes a putative cyanobacteriochrome denoted LcyA, a putative sensor histidine kinase; an allophycocyanin (FRL-AP; ApcD4-ApcB3) that absorbs far-red light; and a putative chlorophyll a-binding protein, denoted IsiX, which is homologous to IsiA. The emergence of FRL absorbance in LL-adapted cells of Synechococcus sp. strain A1463 was analyzed in cultures responding to differences in light intensity. The far-red absorbance phenotype arises from expression of a novel antenna complex containing the FRL-AP, ApcD4-ApcB3, which is produced when cells were grown at very low irradiance. Additionally, the two GAF domains of LcyA were shown to bind phycocyanobilin and a [4Fe-4S] cluster, respectively. These ligands potentially enable this photoreceptor to respond to a variety of environmental factors including irradiance, redox potential, and/or oxygen concentration. The products of the gene clusters specific to LL-ecotypes likely facilitate growth in low-light environments through a process called Low-Light Photoacclimation.

Diversity and Evolution of Pigment Types in Marine Synechococcus Cyanobacteria.

Synechococcus cyanobacteria are ubiquitous and abundant in the marine environment and contribute to an estimated 16% of the ocean net primary productivity. Their light-harvesting complexes, called phycobilisomes (PBS), are composed of a conserved allophycocyanin core, from which radiates six to eight rods with variable phycobiliprotein and chromophore content. This variability allows Synechococcus cells to optimally exploit the wide variety of spectral niches existing in marine ecosystems. Seven distinct pigment types or subtypes have been identified so far in this taxon based on the phycobiliprotein composition and/or the proportion of the different chromophores in PBS rods. Most genes involved in their biosynthesis and regulation are located in a dedicated genomic region called the PBS rod region. Here, we examine the variability of gene content and organization of this genomic region in a large set of sequenced isolates and natural populations of Synechococcus representative of all known pigment types. All regions start with a tRNA-PheGAA and some possess mobile elements for DNA integration and site-specific recombination, suggesting that their genomic variability relies in part on a “tycheposon”-like mechanism. Comparison of the phylogenies obtained for PBS and core genes revealed that the evolutionary history of PBS rod genes differs from the core genome and is characterized by the co-existence of different alleles and frequent allelic exchange. We propose a scenario for the evolution of the different pigment types and highlight the importance of incomplete lineage sorting in maintaining a wide diversity of pigment types in different Synechococcus lineages despite multiple speciation events.

Synechococcus silicon accumulation in oligotrophic oceans

AbstractSi accumulation by Synechococcus, small unicellular marine picocyanobacteria that dominate in nutrient‐depleted waters, is significant due to its potential to alter our understanding of the global Si cycle. To date, however, there are only a few studies on Si accumulation in individual Synechococcus cells. To determine the magnitude and variability of Synechococcus cellular Si content in oligotrophic oceans, we analyzed 1348 discrete cells collected from the understudied eastern Indian Ocean (EIO) and western Pacific Ocean (WPO). Synechococcus cellular Si quotas varied widely across both regions, ranging from 0 to 4651 amol Si cell−1. While highly variable in range, average Si quotas were ~ 2.5‐fold lower in Synechococcus cells from the EIO (172 ± 304 amol Si cell−1) than in those from the WPO (438 ± 737 amol Si cell−1). The estimated contributions of Synechococcus to total and picoplankton biogenic Si stocks were < 1–8% and 1–11%, respectively, suggesting that Synechococcus has a small but persistent regional contribution to biogenic Si stocks. Here, we also made a first‐order estimate of the Synechococcus biogenic Si stock for the global ocean, that is, 0.06–0.09 Tmol Si, accounting for 2–3% of the global ocean diatom Si stock. No significant effects of temperature and dissolved inorganic N and P on cellular Si quotas were observed within these oligotrophic ecosystems. However, salinity, ambient dissolved Si, and N/P ratio were closely correlated with the variable Si quotas with different relationships. In addition, Synechococcus cellular Si/P and Si/S ratios associated with physiological processes were significantly influenced by environmental and geographic variables. We thus suggest that the variance in cellular Si quotas may be indirectly driven by ambient variables via some unknown independent or strain‐dependent physiological processes.

Acid-base properties of Synechococcus-derived organic matter

Marine cyanobacteria play an important role in trace metal cycling in the oceans. However, the influence of bacterial detritus following cell lysis – that includes both particulate organic matter (POM) and dissolved organic matter (DOM) – is less understood. Previous investigations have shown that the ratio of bacterial detritus to living cells increases significantly with ocean depth, indicating that the former plays a central role in trace metal cycling and eventual sequestration in deep marine sediments. Thus, in this study we produced detritus from the mechanical lysis of the common marine cyanobacterium Synechococcus sp. PCC 7002 (referred to as cyPOM and cyDOM), and then measured their buffering capacity through proton adsorption and release via potentiometric acid-base titrations. Both cyPOM and cyDOM were best modelled using a 2-site non-electrostatic protonation model. The cyPOM fraction possessed ligands with pKa values of 5.78 (±0.07) and 9.01 (±0.29) with corresponding site concentrations of 41.8 (±8.15) µmol g−1 and 41.2 (±5.28) µmol g−1, while cyDOM had pKa values of 4.89 (±0.22) and 6.80 (±0.22) and corresponding site concentrations of 42.8 (±14.6) µmol g−1 and 37.3 (±16.5) µmol g−1. As a comparison, intact Synechococcus cells were previously reported to be best modelled by invoking 3-sites with overall ligand densities more than double that of cyPOM and cyDOM. Trace metal (Cd, Co, Cu, Ni, and Zn) adsorption experiments indicate that cyPOM has a lower affinity towards trace metals than intact Synechococcus cells, evidenced by lower trace metals adsorption per gram of dry mass and therefore less trace metal sequestration potential. This implies that intact Synechococcus cells are chiefly responsible for trace metal sequestration, even at high cyPOM proportions (10:1 – cyPOM:Synechococcus) that are more representative of POM that reaches the seafloor. The cyDOM-trace metal association could not be determined experimentally; thus we applied existing thermodynamic data from modern marine DOM studies acquired via potentiometric titrations and metal-binding constants. Unlike cyPOM, metal speciation is almost entirely accounted for in the dissolved fraction (>99.9%). These results further the view that DOM is the most important microbial fraction in controlling metals speciation in the water column.

Evaluation of potent cyanobacteria species for UV-protecting compound synthesis using bicarbonate-based culture system.

The present investigation evaluates the potential of three cyanobacteria species Anabaena cylindrica, Nostoc commune and Synechococcus BDUSM-13 for photo-protecting mycosporine-like amino acids (MAAs) synthesis using bicarbonate-based culture system. Current investigations witnessed noteworthy bicarbonate tolerance of all species (NaHCO3; 0.5, 1 and 2gL- 1) in terms of their growth rate, chlorophyll content, biomass productivity and carbon fixation ability. Among all strains, Synechococcus BDUSM-13 showed maximum surge in specific growth rate (i.e. 0.72 day-1) at 1gL-1, productivity (i.e. 0.92 ± 0.06g day-1L-1) and chlorophyll content (i.e. 0.09gL-1) at 2g day-1L-1. Synechococcus cells were also has the 0.48gdw-1 carbon content with highest CO2 fixation rate (i.e. 0.653g.CO2mL-1day-1) at 2gL-1. Though, they were not able to produce MAAs after long UV-B exposure (i.e. 24 and 48h). A. cylindrica strain was the most competent species for the bicarbonate-based approach, produced UV-protecting iminomycosporine compound (i.e. shinorine, λ max at 334 ± 2nm) along with carbon fixation (i.e. 0.49gCO2mL-1day-1) at 2gL-1 NaHCO3. This suggests the bicarbonate supplementation during cultivation is a promising strategy to increase cellular abundance, biomass productivity and carbon fixation in cyanobacteria. However, UV-B irradiation may cause species-specific differences in the MAAs synthesis to produce UV-protecting compounds.

Diazotroph-Derived Nitrogen Assimilation Strategies Differ by Scleractinian Coral Species

Reef-building corals generally thrive in nutrient-poor tropical waters, where among other elements, nitrogen (N) availability often limits primary productivity. In addition to their close association with endosymbiotic dinoflagellates of the family Symbiodiniaceae, enabling an effective use and retention of dissolved inorganic nitrogen (DIN), scleractinian corals have developed strategies to acquire new N: (1) They can ingest N-rich sediment particles and preys (from picoplankton to macro-zooplankton) via heterotrophy, including diazotrophs [plankton fixing dinitrogen (N2) and releasing part of this nitrogen—Diazotroph-Derived N (DDN)—in seawater], a pathway called “heterotrophic nutrition on diazotrophs”; (2) Symbiotic diazotrophs located in the coral holobiont have the molecular machinery to fix N2, a pathway called “symbiotic N2 fixation”. Here we used the 15N2 isotopic labeling in a series of incubations to investigate the relative contribution of each of these DDN transfer pathways in three worldwide distributed coral species: Acropora muricata, Galaxea fascicularis, and Pocillopora damicornis. We show that N provision via “symbiotic N2 fixation” is negligible compared to that obtained via “heterotrophic nutrition on diazotrophs,” with DDN assimilation rates about a thousand times lower for P. damicornis and G. fascicularis, or assimilation rates via “symbiotic N2 fixation” almost nil for A. muricata. Through heterotrophic feeding on planktonic diazotrophs, only G. fascicularis and P. damicornis can successfully obtain N and fulfill a large part of their N requirements (DDN asimilation rates: 0.111 ± 0.056 and 0.517 ± 0.070 μg N cm–2 h–1 in their Symbiodiniaceae, respectively). Whereas this contribution is again negligible for A. muricata. They also largely consume the picoplankton that likely benefit from this DDN (Prochlorococcus and Synechococcus cells; respectively, 2.56 ± 1.57 104 and 2.70 ± 1.66 104 cell h–1 cm–2 for G. fascicularis; 3.02 ± 0.19 105 and 1.14 ± 0.79 104 cell h–1 cm–2 for P. damicornis). The present study confirms the different dependencies of the three tested species regarding heterotrophy, with P. damicornis and G. fascicularis appearing highly efficient at capturing plankton, while A. muricata, considered as mainly autotroph, does not rely on these food resources to meet its N and energy needs.

Spatial Distribution of Picophytoplankton in Southeastern Coast of Peninsular Malaysia Using Flow Cytometry

The distribution of picocyanobacteria from two genera, Synechococcus and Prochlorococcus, and picoeukaryotes in surface water (0.5 m) was investigated by flow cytometry in the southeastern coast of Peninsular Malaysia during the Southwest monsoon in August 2014. During the cruise, Synechococcus cells were predominant throughout the study area, contributing as much as 50% to the total picophytoplankton population, whereas picoeukaryotes and Prochlorococcus constituted only 31% and 19% of the population, respectively. Spatially, Synechococcus and picoeukaryotes were more dominant in coastal waters, while Prochlorococcus appeared to be more highly abundant in offshore waters. Furthermore, the percentage contribution of each population to total picophytoplankton also exhibited different spatial distribution patterns along a coastal-offshore gradient. The percentage contribution of Synechococcus was spatially constant throughout the study area, while the fraction contributed by picoeukaryotes showed a reduced contribution from coastal to offshore waters. In contrast, Prochlorococcus exhibited an increased proportion to total picophytoplankton across a coastal-offshore gradient, suggesting the increasing importance of this population in offshore waters of the study area. As revealed by Canonical Correlation Analysis, the abundance of Synechococcus and picoeukaryotes increased significantly with reducing dissolved oxygen levels and pH, and with increasing total chlorophyll. In contrast, temperature was the only factor influencing the abundance of Prochlorococcus significantly increased with decreasing water temperature in the study area. Overall, results of the present study provide valuable information on the role of regional environmental factors in the distribution and dominance of picophytoplankton communities that are not only critical for the ocean productivity but also the impact on the carbon cycle in the study area.

Dynamics and Distribution of Marine Synechococcus Abundance and Genotypes during Seasonal Hypoxia in a Coastal Marine Ranch

Marine Synechococcus are an ecologically important picocyanobacterial group widely distributed in various oceanic environments. Little is known about the dynamics and distribution of Synechococcus abundance and genotypes during seasonal hypoxia in coastal zones. In this study, an investigation was conducted in a coastal marine ranch along two transects in Muping, Yantai, where hypoxic events (defined here as the dissolved oxygen concentration <3 mg L−1) occurred in the summer of 2015. The hypoxia occurred in the bottom waters from late July and persisted until late August. It was confined at nearshore stations of the two transects, one running across a coastal ranch and the other one outside. During this survey, cell abundance of Synechococcus was determined with flow cytometry, showing great variations ranging from 1 × 104 to 3.0 × 105 cells mL−1, and a bloom of Synechococcus occurred when stratification disappeared and hypoxia faded out outside the ranch. Regression analysis indicated that dissolved oxygen, pH, and inorganic nutrients were the most important abiotic factors in explaining the variation in Synechococcus cell abundance. Diverse genotypes (mostly belonged to the sub-clusters 5.1 and 5.2) were detected using clone library sequencing and terminal restriction fragment length polymorphism analysis of the 16S–23S rRNA internal transcribed spacer region. The richness of genotypes was significantly related to salinity, temperature, silicate, and pH, but not dissolved oxygen. Two environmental factors, temperature and salinity, collectively explained 17% of the variation in Synechococcus genotype assemblage. With the changes in population composition in diverse genotypes, the Synechococcus assemblages survived in the coastal hypoxia event and thrived when hypoxia faded out.

Amino Acid Analog Induces Stress Response in Marine Synechococcus.

Characterizing the cell-level metabolic trade-offs that phytoplankton exhibit in response to changing environmental conditions is important for predicting the impact of these changes on marine food web dynamics and biogeochemical cycling. The time-selective proteome-labeling approach, bioorthogonal noncanonical amino acid tagging (BONCAT), has potential to provide insight into differential allocation of resources at the cellular level, especially when coupled with proteomics. However, the application of this technique in marine phytoplankton remains limited. We demonstrate that the marine cyanobacteria Synechococcus sp. and two groups of eukaryotic algae take up the modified amino acid l-homopropargylglycine (HPG), suggesting that BONCAT can be used to detect translationally active phytoplankton. However, the impact of HPG addition on growth dynamics varied between groups of phytoplankton. In addition, proteomic analysis of Synechococcus cells grown with HPG revealed a physiological shift in nitrogen metabolism, general protein stress, and energy production, indicating a potential limitation for the use of BONCAT in understanding the cell-level response of Synechococcus sp. to environmental change. Variability in HPG sensitivity between algal groups and the impact of HPG on Synechococcus physiology indicates that particular considerations should be taken when applying this technique to other marine taxa or mixed marine microbial communities. IMPORTANCE Phytoplankton form the base of the marine food web and substantially impact global energy and nutrient flow. Marine picocyanobacteria of the genus Synechococcus comprise a large portion of phytoplankton biomass in the ocean and therefore are important model organisms. The technical challenges of environmental proteomics in mixed microbial communities have limited our ability to detect the cell-level adaptations of phytoplankton communities to a changing environment. The proteome labeling technique, bioorthogonal noncanonical amino acid tagging (BONCAT), has potential to address some of these challenges by simplifying proteomic analyses. This study explores the ability of marine phytoplankton to take up the modified amino acid, l-homopropargylglycine (HPG), required for BONCAT, and investigates the proteomic response of Synechococcus to HPG. We not only demonstrate that cyanobacteria can take up HPG but also highlight the physiological impact of HPG on Synechococcus, which has implications for future applications of this technique in the marine environment.

Significant Pico- and Nanoplankton Contributions to Biogenic Silica Standing Stocks and Production Rates in the Oligotrophic Eastern Indian Ocean

The present study involves the first measurements of size-fractionated biogenic silica (bSi) standing stocks and production rates in the oligotrophic Eastern Indian Ocean. The 150-m integrated bSi standing stocks in the pico- and nanosized fractions averaged 49% and 39%, respectively, of the total; the contributions of pico- and nanoplankton to total bSi production rates were 43% and 38%, respectively, together suggesting that these smaller plankton contributed a significant proportion of both the total bSi standing stock and its rate of production. The total bSi variability appeared to be driven by smaller-plankton dynamics. Also, our results suggest that the detrital bSi stocks were potentially sustained by the pico- and nanosized siliceous organisms (for example, Minidiscus and Synechococcus) instead of broken fragments of large diatoms or other siliceous microplankton. In particular, the atomically dense structure from Synechococcus cell lysis was enriched in Si element compared with intact cells. The factors controlling size-fractionated bSi standing stocks may be biological rather than physical processes, and the clear correlation between picoeukaryotes and the < 2 μm bSi further confirmed the possibility of Si accumulation by other smaller plankton.

Relationship between Microorganisms Inhabiting Alkaline Siliceous Hot Spring Mat Communities and Overflowing Water.

The compositions of Octopus Spring and Mushroom Spring (Yellowstone National Park, Wyoming, USA) microbial mats have been thoroughly studied, but the compositions of the effluent waters that flow above the mats have not. In this study, cells in the mats and overflowing waters of both springs were investigated at multiple sites where Synechococcus spp. are the dominant cyanobacteria (ca. 72°C to ca. 50°C), and on several dates. In addition to microscopic analyses of stained and autofluorescent cells, 16S rRNA gene sequencing was used to characterize the major taxa present and a protein-encoding gene (psaA) was sequenced and analyzed by ecotype simulation to predict species of Synechococcus The mats of both springs were similar in terms of the downstream distribution of predominant taxa detected previously. However, waters above these mats were predominated by taxa that reside in upstream mats or communities above the upper-temperature limit of the mat. A disturbance/recolonization study was performed at a site normally predominated by Synechococcus species adapted to low temperatures. After removing indigenous Synechococcus cells, Synechococcus species adapted to higher temperatures, which were predominant in the water overflowing this site, colonized the newly forming mat. Differences in recolonization under reduced and UV-screened irradiance suggested that, in addition to physical transport, environmental conditions likely select for species that are better adapted to these different conditions and can influence mat recovery. A transport model was developed and used to predict that, in Mushroom Spring, erosion predominates in the narrower and deeper upstream effluents and deposition predominates over erosion in wider and shallower downstream effluents.IMPORTANCE In flowing aquatic systems, cell erosion and deposition are important to the dispersal of cells from one location to another. Very little is known about microbial dispersal and the physical processes that underlie it. This study demonstrates its importance to colonization of downstream surfaces and especially to the recolonization and functioning of disturbed sites. Ecological systems in flowing environments are often, roughly speaking, pseudosteady, in that nutrients enter the system and by-products leave at relatively steady rates. Over time, material inputs and outputs must balance. Measurements of input fluxes (e.g., growth rates and proxies, such as photosynthesis rates) are frequent. However, erosion and deposition of cells are seldom measured and ecological significance is sometimes neglected. The importance of these parameters is immediately evident in any attempt to construct a model of long-time community behavior, as spatial ecological structure is significantly impacted and can be dominated by migration of organisms, even in small numbers.

Cadmium adsorption to clay-microbe aggregates: Implications for marine heavy metals cycling

Interactions between microorganisms and clay minerals influence the transport and cycling of metal contaminants in both marine and terrestrial environments. The present study was conducted to quantify the adsorption of dissolved cadmium, Cd(II), under seawater-like conditions to the marine cyanobacterium Synechococcus sp. PCC 7002, three common clay minerals (kaolinite, montmorillonite and illite), as well as cell-clay aggregates. We show here that the Synechococcus-only experiments removed the most Cd above pH 5.5, followed in decreasing order by aggregates of 50% cells:50% individual clays, aggregates of cells and all 3 clays, and individual clays. Electron microscope imaging showed that clays associated in a tangential edge-on orientation to the cells in Synechococcus-clay mineral aggregates. A non-electrostatic surface complexation modeling approach was used to fit Cd adsorption onto Synechococcus cells and individual clay minerals. The resulting Cd binding constants were then used in consort with surface functional group pKa values and site concentrations to accurately predict the extent of Cd adsorption onto the Synechococcus-clay mineral aggregates using the component additivity (CA) approach. We observed that the addition of cyanobacterial cells to clay mineral suspensions led to significantly larger mean aggregate sizes of clay minerals, enhancing the clay sedimentation rate. Although specifically focused on Cd, our study indicates that the ratio of bacterial plankton to clay minerals is an important determinant in terms of understanding the rate with which metals are transferred from the water column to the seafloor.

Diel, daily, and spatial variation of coral reef seawater microbial communities.

Reef organisms influence microorganisms within the surrounding seawater, yet the spatial and temporal dynamics of seawater microbial communities located in proximity to corals are rarely investigated. To better understand reef seawater microbial community dynamics over time and space, we collected small-volume seawater samples during the day and night over a 72 hour period from three locations that differed in spatial distance from 5 Porites astreoides coral colonies on a shallow reef in St. John, U.S. Virgin Islands: near-coral (sampled 5 cm horizontally from each colony), reef-depth (sampled 2 m above each colony) and surface seawater (sampled 1 m from the seawater surface). At all time points and locations, we quantified abundances of microbial cells, sequenced small subunit rRNA genes of bacterial and archaeal communities, and measured inorganic nutrient concentrations. Prochlorococcus and Synechococcus cells were consistently elevated at night compared to day and these abundances changed over time, corresponding with temperature, nitrite, and silicate concentrations. During the day, bacterial and archaeal alpha diversity was significantly higher in reef-depth and near-coral seawater compared to the surface seawater, signifying that the reef influences the diversity of the seawater microorganisms. At night, alpha diversity decreased across all samples, suggesting that photosynthesis may favor a more taxonomically diverse community. While Prochlorococcus exhibited consistent temporal rhythmicity, additional taxa were enriched in reef seawater at night compared to day or in reef-depth compared to surface seawater based on their normalized sequence counts. There were some significant differences in nutrient concentrations and cell abundances between reef-depth and near-coral seawater but no clear trends. This study demonstrates that temporal variation supersedes small-scale spatial variation in proximity to corals in reef seawater microbial communities. As coral reefs continue to change in benthic composition worldwide, monitoring microbial composition in response to temporal changes and environmental fluctuations will help discern normal variability from longer lasting changes attributed to anthropogenic stressors and global climate change.